A Text-book of Paper-making. C. F. Cross
at 60°–80° C. (140°–176° F.), a considerable portion of the fibre substance is dissolved. The action of either reagent is of course purely hydrolytic; and the hydrolysis is of the simplest character, since the substance dissolved as well as the residual fibre are found to have the same percentage composition. Moreover, the residual fibre, though having undergone a profound structural modification, and having been converted into a disintegrated mass of brittle fragments, still preserves the chemical characteristics of the original, unaltered. Thus it is converted by the action of chlorine into a similar complex of derivatives, yielding on resolution by sodium sulphite solution 75 per cent. of cellulose; also when acted upon by alkaline hypobromite it yields bromoform. Under the action of these hydrolytic reagents, therefore, the fibre shows itself to be essentially a chemical whole. At the boiling temperature, these acids resolve as well as dissolve the fibre substance, and the volatile products are acetic acid and the peculiar aldehyde {21} furfural C4H3O.COH. The yield of this aldehyde may be raised with suitable precautions to 15–20 per cent. of the raw fibre. The action of dilute nitric acid upon the fibre differs from that of the above-mentioned acids, in effecting its resolution into soluble derivatives and insoluble cellulose; the yield of the latter when the reaction is conducted at 60° C. (140° F.), with 5 parts HNO3 is 60 per cent. only, showing that in the process of isolation some of the cellulose itself is attacked and converted into soluble products.
Schulze’s method of isolating cellulose from wood, and from the ligno-celluloses generally, consisted in macerating them for 12 to 14 days with 8⁄10 their weight of potassium chlorate dissolved in 12 parts by weight of nitric acid (sp. gr. 1·10), and completing the resolution by afterwards boiling with dilute ammonia. By the action of a more concentrated acid, 50 per cent. HNO3, at 80° C. (176° F.), a soluble derivative is obtained which has the composition (C25H40NO25). It is a syrupy, highly acid body, dyeing animal fibres a deep yellow shade, and giving with the earthy bases salts of the formula (C25H32NO25M4), which are precipitated by alcohol from their aqueous solution in the form of bright yellow flocks that dry to a yellow powder.
Dilute Alkalis.
—The action of boiling dilute solutions of the caustic alkalis upon the ligno-celluloses is similar to that of the dilute acids, viz., purely hydrolytic, causing no essential change in the composition of the fibre substance.
Water at High Temperatures.
—The ligno-celluloses undergo a profound modification when heated with water at elevated temperatures. They are to a great extent converted into soluble products, of which a large proportion are the volatile bodies, acetic and formic acids and furfural. The residual fibre is found to be more or less disintegrated, and of a dark-brown colour, but preserving many of the chemical features of the original. A similar disintegration is caused by exposing the ligno-celluloses in a dry state to an atmosphere of superheated steam, the effect being much increased if the ligno-cellulose be previously bleached by any of the ordinary {22} processes, i.e., under oxidising conditions. In these decompositions oxidation, as well as hydration, plays an important part. It is found that the presence of small quantities of reducing agents, e.g., sulphites, exerts a remarkable effect in retarding and often entirely preventing these changes. It is probable that they act in obviating an initial change, which, with a cumulative reaction on the fibre, effects the profound resolutions above described. (See p. 71.)
Concentrated Hydrochloric Acid.
—When exposed to the concentrated aqueous acid at ordinary temperatures, ligno-cellulose undergoes a profound structural modification, and is largely converted into soluble bodies. The disintegrated residue reacts with chlorine similarly to the original jute, but the quantity of cellulose isolated by subsequent treatment with alkaline solutions is only 50 per cent. of the original. Since jute cellulose, after isolation, exhibits under similar treatment a much smaller conversion into soluble products, 10 per cent. as compared with 33, we have here further evidence that the cellulose is present in the fibre in a condition chemically different from that of the isolated cellulose.
Sulphuric Acid.
—On triturating the fibre with the concentrated acid, it dissolves to a brownish-purple solution; on pouring this solution into water, a substance is precipitated in dark-brown flocks; when dried it has the following composition:
| C | 64·4 |
| H | 4·4 |
| O | 31·2 |
The solution yields on distillation furfural and acetic acid.
Nitric and Sulphuric Acids.
—(1 : 2 by vol.)—By the action of these acids ligno-cellulose is converted into yellow-coloured explosive compounds, preserving all the external features of the original fibre, and showing a close resemblance to the pyroxylins.
The increase in weight resulting from the fixation of the {23} nitric acid residue is approximately equal to that of cotton “nitrated” under the same conditions.
They are freely soluble in acetone. On examination they prove to be homogeneous. If the fibre be warmed with the mixture after the first reaction is completed, it dissolves. The solution is found to contain oxalic, succinic, and suberic acids, but no aromatic nitro-derivatives, whereas if ligno-cellulose contain a benzene nucleus, as has been supposed, such derivatives could not fail to be formed under these conditions.
Animal Digestion of Ligno-cellulose.
—It has long been known that the urine of herbivorous animals contains hippuric acid, or benzoyl glycocine, as a normal constituent, and it has been shown that the benzoyl radicle necessary to form this body by reacting with the glycocine of the liver, is a product of the digestion of ligno-cellulose. On the other hand, it has been shown that ligno-cellulose contains no benzene compounds as such. We have therefore, in this fact additional evidence that a portion of the complex ligno-cellulose molecule is in what we may term a potentially aromatic condition.
Distribution of Ligno-celluloses.
—As already indicated, the distribution of the ligno-celluloses is extremely wide; they are met with in every variety of vegetable tissue, and their presence is readily ascertained by the reaction of chlorination already described. Of these ligno-celluloses most closely allied to jute, we may mention the stony concretions of pears (glycodrupose) and the main tissue of fir wood (glycolignose).
Decay of Ligno-cellulose.